Multifocal magnetron design for physical vapor deposition processing on a single cathode

ABSTRACT

An apparatus has a keeper plate with a keeper plate outer perimeter. An annular magnet array with an annular magnet array outer perimeter is coincident with the keeper plater outer perimeter. An inner top magnet is positioned on a centerline of a first side of the keeper plate and an inner bottom magnet is positioned on the centerline of a second side of the keeper plate. The inner top magnet is of a first magnetic orientation and the annular magnet array and the inner bottom magnet have a second magnetic orientation opposite the first magnetic orientation to form a magnetic field environment that provides plasma confinement of ionizing electrons which causes a gas operative as a reactive gas and sputter gas to become ionized and subsequently be directed to a target cathode while simultaneously causing the ionization of sputtered species which are dispersed across a substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 16/210,488, filed Dec. 5, 2018, which claims priority to U.S.Provisional Patent Application No. 62/598,383, filed Dec. 13, 2017, thecontents of each application are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to material processing. Moreparticularly, this invention relates to an apparatus for physical vapordeposition sputter processing of thin film materials.

BACKGROUND OF THE INVENTION

Sputter processing has been the preferred mode of operation for manythin film deposition processes owing to its cost effectiveness and easein process design. To make most use of the technology, magnetrons havebeen employed which enable effective confinement of electron plasmasnear the target cathode at low operating pressures (<10 mTorr). This isaccomplished by placing a magnet or magnet array of one polarity andsurrounding it with a magnet of the opposite polarity. In so doing,magnetic field lines traverse through space from one magnet to theother. Torque is provided to electrons as they orbit the changing vectorof the connecting fields, which is found maximum at that point when thefield is orthogonal to the original direction of travel (zero-crossing).With this amount of torque, the orbiting electron reaches a zenith inquantum mechanical cross-section and is optimized to ionize proximalvapor species.

FIG. 1A illustrates two annular magnet arrays 40 and 42 connected to apermeable keeper plate 41. The device as integrated is shown inperspective in FIG. 1B. Similarly, in FIG. 2A a single center magnet 102is surrounded by an oppositely polarized magnet 101 and both areconnected to a keeper plate 100. The device is shown in perspective inFIG. 2B.

One limitation of these magnetrons as described is that the outer magnet(e.g., 40 or 101) will necessarily form a fringing field allowing thebalance of the flux not absorbed by the inner magnet (e.g., 42 or 102)to close back to the other pole. This fringing field causes thedivergence of fast electrons (i.e., those of ionizing energies) awayfrom the desired confinement zone within which ionization would lead toimpact sputtering. This is shown graphically in FIG. 1A. The divergenceis represented by the dashed line (43) which indicate where thezero-crossing may be found as one traverses spatially above themagnetron surface. Furthermore, when a plurality of other such devicesare brought into proximity of each other, the electron dynamics causeincreasing levels of interference to stable operation of the individualsputter plasmas.

SUMMARY OF THE INVENTION

An apparatus has a keeper plate with a keeper plate outer perimeter. Anannular magnet array with an annular magnet array outer perimeter iscoincident with the keeper plater outer perimeter. An inner top magnetis positioned on a centerline of a first side of the keeper plate and aninner bottom magnet is positioned on the centerline of a second side ofthe keeper plate. The inner top magnet is of a first magneticorientation and the annular magnet array and the inner bottom magnethave a second magnetic orientation opposite the first magneticorientation to form a magnetic field environment that provides plasmaconfinement of ionizing electrons which causes a gas operative as areactive gas and sputter gas to become ionized and subsequently bedirected to a target cathode while simultaneously causing the ionizationof sputtered species which are dispersed across a substrate.

BRIEF DESCRIPTION OF THE FIGURES

The invention is more fully appreciated in connection with the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1A is a cross section of a simple magnetron magnet pack withoppositely polarized magnets mounted concentrically atop a keeper plate41.

FIG. 1B is a perspective drawing of the same fully integrated part ofFIG. 1A.

FIG. 2A is a cross section of a simple magnetron magnet pack with acenter magnet 102 surrounded by an oppositely polarized magnet 101. Bothmagnets are connected to a keeper plate 100.

FIG. 2B is a perspective view of the device of FIG. 2A.

FIG. 3A is a detailed drawing in cross section of the new magnet packassembly 11 incorporated into a functional magnetron structure.

FIG. 3B a perspective view of the device of FIG. 3A.

FIG. 4A is a cross sectional view of the novel magnet pack showing thearrangement of magnet arrays and the resultant field vectors andprojection of zero-crossings.

FIG. 4B is a perspective drawing of the device of FIG. 4A.

FIG. 5 is a cross sectional drawing of a similar magnet pack structurewith magnet arrangement suitable for small cathode dimensions.

FIG. 6 is a cross sectional schematic showing the incorporation of themagnet pack within a functioning magnetron structure.

FIG. 7 is a schematic showing proximal placement of two devices and howthey would maintain relative independence from a magnetic fieldperspective from each other.

DESCRIPTION OF THE INVENTION

FIG. 3A illustrates a magnet pack 11 constructed in such a way that themagnetic field is propagated primarily from the inner portion of themagnet pack to the outer edge of the magnet pack. Furthermore, theprojection of resultant zero-crossings of the magnetic field lines(i.e., where the field is directly parallel to the magnet emanatingsurface 6 as well as parallel with the cathode surface 1 are observed tobe collinear with the axis normal of cathode or are found increasinglytoward centerline of the magnet pack 11.

This is shown in FIG. 4A. The projection of zero-crossings in thisfigure are shown as 13. Returning to FIG. 3A, the magnets comprising themagnet pack 11 are situated such that the inner array is mounted on topof a permeable keeper plate assembly 3 (μ/μ₀˜1000) and positioneddirectly beneath a cathode structure which is comprised of a slab oftarget material 1 from which the deposition will be derived. The cathodetarget 1 is affixed to a heat-sinking element 4 that is electrically aswell as thermally connected to the target. The keeper plate assembly 3is made sufficiently thick that pass through magnetic flux from any ofthe magnet arrays described in this document is substantially inhibited.Additionally, the keeper plate is designed with intentional shape anddimension to effectuate the following phenomena: that the flux emanatingfrom the top inner magnet array is propelled substantially perpendicularto the emanating surface as well as substantially away from the centerof the magnet pack; and that the return flux from the inner magnet arraybe found at its highest reverse intensity at the outer edge of thekeeper plate assembly. The combination of these effects will ensure thedesired outcome as described above relative to the envelope ofzero-crossings of the magnetic field. The field density at the outeredge of the keeper plate serves as the field confinement edge forensuing plasmas above the cathode.

To improve the confinement capability, a magnet array 2 is placed belowthe keeper plate 3 such that it is found on the opposite surface withrespect to the top inner magnet array 6. The lower outer magnet array 2is maintained at or near the outer perimeter of the keeper plate 3. Thelower outer magnet array 2 is opposite in magnetic polarity to the topsurface inner magnet array 6. In this way, the returning magnetic fluxemanating from the top surface inner magnet array 6 is focused to asubstantial field intensity at the outer edge of the keeper plateassembly 3. Moreover, the fringing return field for the lower surfaceouter magnet array 2 is substantially away from the top surface innerarray and does not constructively or destructively interact appreciablywith the field emanating from the top surface inner magnet array 6.

A second lower surface (of the keeper plate assembly) inner magnet array5 that is at a similar radius to the top surface inner magnet array isadded that is parallel in magnetic polarity to the bottom surface outermagnet array 2. It is found that the presence of this bottom surfaceinner magnet array 5 is supportive to a high confinement field densityat the outer edge of the keeper plate assembly 3.

The combination of these elements of the magnet pack design allow thepropagation of magnetic field zero-crossings to be convergent about theinner portion of the cathode structure above. This promotes theenlargement of the spatial section above the cathode in which there isionization of vapor species. To further this effect, the magnetic fieldis designed such that the flux emanating from the top surface innermagnetic array is substantially higher than the flux density measured atthe plasma confinement edge demarcated by the keeper plate assembly (aspreviously described). Specifically, it is observed that the top innermagnet array 6 produces at least 150% flux intensity and more preferably300% flux intensity measured at the plasma confinement outer edge.

The magnetron as deployed to facilitate the deposition of material in avacuum environment. In FIG. 3A, the spatial relationship of individualpiece parts as integrated is shown. The cathode 1 and heatsink 4 areclamped to a vacuum mounting flange 7 which is connected to a vacuumsystem (not shown). The material vaporized is collected by anintentional substrate 12 and chamber shield 8. On the atmospheric sideof the device is a facilities water connection 9 for the supply ofcoolant to the heatsink. Also, in this embodiment, a wheel base 10 isattached to the outside of the structure that facilitates convenience inattaching the tool to the vacuum system. FIG. 3B is a perspective viewof the device of FIG. 3A.

FIG. 4A illustrates keeper plate 3, lower outer magnetic array 2 andlower inner magnetic array 5. The figure also illustrates the top innermagnetic array 6. The figure also illustrates flux lines. Zero crossingsare shown at the position marked 13. FIG. 4B is a perspective view ofthe lower outer magnetic array 2, keeper plate 3 and top inner magneticarray 6.

The disclosed technology has been applied to a magnetron where the sizeof the tool has called for the use of a top surface inner magnet array 6that may be a tubular annulus magnet that facilitates the larger targetsize. The technology is also conducive for smaller size operation.

FIG. 5 illustrates an embodiment optimized for a smaller configuration.An inner top surface magnet 20 is placed collinear with the devicecenterline. The keeper plate assembly 21 is shown in this embodiment ashaving a tapered edge protruding from the outer edge upward. An annularmagnet array 22 is connected to the bottom surface of the keeperassembly 21 and the magnetic polarity of this array 22 is opposite tothe top magnet 20. As was found for the larger device, it is found to beuseful to include a second magnet array (or singular magnet) 23 to thebackside of the keeper 21 affixed magnetically and positionedcollinearly to the centerline of the device. In this embodiment 28, wehave demonstrated that a stack of magnets of decreasing radius may beused appropriately as the backside array 23.

FIG. 6 shows how the embodiment 28 could be incorporated in a magnetronstructure to facilitate the deposition of material in a vacuumenvironment. In this case, the substrate 29 is shown in relation to thecross section of the magnetron. The target 30 is attached to aheat-sinking element 24 which is supplied with coolant through afacilities nozzle 27. A clamp ring shield 25 is applied over the exposedheat-sinking element 24 that inhibits build-up of vapor material uponthe element 24. An enclosure provided for safety purposes surrounds theportion of the device that is exposed to the atmospheric side of thetool and is shown as 26.

When one such magnetron device 28 is placed directly behind a cathodeassembly, it is thus observed that very low fringing field occurs beyondthe perimeter of the device assembly. Therefore, it is then possible toplace a plurality of such devices proximally to each other that willeach define an independent plasma zone above the target. This is shownin FIG. 7 . Therein, film uniformity may be tailored by judiciousplacement of individual magnet packs across a cathode surface.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the invention.However, it will be apparent to one skilled in the art that specificdetails are not required in order to practice the invention. Thus, theforegoing descriptions of specific embodiments of the invention arepresented for purposes of illustration and description. They are notintended to be exhaustive or to limit the invention to the precise formsdisclosed; obviously, many modifications and variations are possible inview of the above teachings. The embodiments were chosen and describedin order to best explain the principles of the invention and itspractical applications, they thereby enable others skilled in the art tobest utilize the invention and various embodiments with variousmodifications as are suited to the particular use contemplated. It isintended that the following claims and their equivalents define thescope of the invention.

1. An apparatus, comprising: a keeper plate with a keeper plate outerperimeter; an annular magnet array with an annular magnet array outerperimeter coincident with the keeper plater outer perimeter; and aninner top magnet positioned on a centerline of a first side of thekeeper plate and an inner bottom magnet positioned on the centerline ofa second side of the keeper plate; wherein the inner top magnet is of afirst magnetic orientation and the annular magnet array and the innerbottom magnet have a second magnetic orientation opposite the firstmagnetic orientation to form a magnetic field environment that providesplasma confinement of ionizing electrons which causes a gas operative asa reactive gas and sputter gas to become ionized and subsequentlydirected to a target cathode while simultaneously causing the ionizationof sputtered species which are dispersed across a substrate.
 2. Theapparatus of claim 1 wherein return flux from the inner top magnet has ahighest reverse intensity halfway between the inner top magnet and anouter edge of the keeper plate assembly.
 3. The apparatus of claim 1wherein flux from the annular magnet array does not appreciably interactwith flux from the inner top magnet.